The present invention relates to a combuster for an industrial gas turbine and, more particularly, to a multi-stage combustion type combustor providing a low nitrogen oxides (NO.sub.x) concentration in an exhaust gas.
As an example of conventional combustors, FIG. 1 of European Patent Publication No. 0 169 431 illustrates a two-stage combustion type combustor, wherein the NO.sub.x concentration in an exhaust gas of this combustor is lower than in a single-stage combustion type combustor. Additionally, FIG. 1 of U.S. Pat. No. 4,112,676 illustrates an example of a combustor providing diffusion combustion while controlling the flow rate of a fuel and multi-stage premix combustion on a downstream side thereof.
Recently, for environmental protection extremely strict regulations for the emission of NO.sub.x have been proposed and such regulations cannot be satisfied by merely employing conventional systems such as described above. Therefore, a more precise control of a combustion phenomenon is necessary.
Of the two conventional systems referenced above, the former proposal reduces the NO.sub.x concentration by a combination of diffusion combustion and premix combustion. However, since diffusion combustion is partially used, the occurrence of hot spots is unavoidable. In order to further reduce the NO.sub.x concentration, an improvement in the diffusion combustion process is necessary.
The latter proposal employs multi-stage premix combustion on the downstream side, but since the diffusion combustion system is employed at the head portion, there is an inevitable limit to the reduction of the NO.sub.x concentration; therefore, practical problems will develop.
Japanese Patent Laid-Open No. 57-41524/1982 discloses a gas turbine in which a premixing chamber is provided outside the combustor for premixing fuel with air that an air from a compressor is boosted up and supplies the resultant premixture into a combustion chamber at a head portion to form a pilot flame, and premixed fuel and air is further supplied on a downstream side thereof for main combustion.